Fault location system using voltage or current measurement from diverse locations on a distribution network

ABSTRACT

A method for identifying a location of a fault in an electrical power distribution network that includes identifying an impedance of an electrical line between each pair of adjacent utility poles, measuring a voltage and a current of the power signal at a switching device during the fault, and estimating a voltage at each of the utility poles downstream of the switching device using the impedance of the electrical line between the utility poles and the measured voltage and current during the fault. The method calculates a reactive power value at each of the utility poles using the estimated voltages, where calculating a reactive power value includes compensating for distributed loads along the electrical line that consume reactive power during the fault, and determines the location of the fault based on where the reactive power goes to zero along the electrical line.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of priority from the U.S.Provisional Application No. 62/823,117, filed on Mar. 25, 2019, thedisclosure of which is hereby expressly incorporated herein by referencefor all purposes.

BACKGROUND Field

The present disclosure relates generally to a method for identifying thelocation of a fault in an electrical power distribution network and,more particularly, to a method for identifying the location of a faultin an electrical power distribution network that includes estimating thevoltages at the utility poles downstream of a last recloser before thefault and compensating for distributed loads.

Discussion of the Related Art

An electrical power distribution network, often referred to as anelectrical grid, typically includes a number of power generation plantseach having a number of power generators, such as gas turbine engines,nuclear reactors, coal-fired generators, hydro-electric dams, etc. Thepower plants provide a high voltage AC signal on high voltagetransmission lines that deliver electrical power to a number ofsubstations typically located within a community, where the voltage isstepped down to a medium voltage. The substations provide the mediumvoltage power to a number of three-phase feeder lines. The feeder linesare coupled to a number of lateral lines that provide the medium voltageto various transformers, where the voltage is stepped down to a lowvoltage and is provided to a number of loads, such as homes, businesses,etc.

Periodically, faults occur in the distribution network as a result ofvarious things, such as animals touching the lines, lightning strikes,tree branches falling on the lines, vehicle collisions with utilitypoles, etc. Faults may create a short-circuit that reduces the load onthe network, which may cause the current flow from the substation tosignificantly increase, for example, up to 2500 amps, along the faultpath. This amount of current causes the electrical lines tosignificantly heat up and possibly melt, and also could cause mechanicaldamage to various components in the substation and in the network.

Many times the fault will be a temporary or intermittent fault asopposed to a permanent or bolted fault, where the thing that caused thefault is removed a short time after the fault occurs, for example, alightning strike, where the distribution network will almost immediatelybegin operating normally. Permanent faults need to be cleared so thatelectrical power can be restored to the section of the networkexperiencing the service outage. Temporary faults often need to beaddressed to prevent the root cause of the fault from escalating into apermanent fault as well as increase the power quality and prevent wearon the equipment. This typically requires a field crew to identify thelocation of the fault and then make the repairs. Permanent faults can beeventually found by the field crew, however, the time it takes to findthe fault can be considerable. Temporary faults are often very difficultto find, and utility companies may decide to ignore such faults untilthey escalate to permanent faults.

As mentioned, in order to clear a fault, the location of the fault mustbe identified. In order for a field crew or other personnel to identifythe location of the fault, they need to know the general location of thefault in order to begin their search. Fault location systems forelectric distribution networks do exist in the art, and typically relyon voltage and current measurements taken at a single location in thenetwork, which is typically at a substation. These fault locationsystems also require the line impedance to be calculated in advance andprovided by the utility company. However, such systems can result inlarge errors between the estimated fault location and the true faultlocation. Further, these systems may produce several candidate faultlocations spread throughout the network. Thus, the value of known faultdetection systems is limited in their ability to accurately identify thelocation of faults. What is needed is a fault location detection methodfor an electrical power distribution network that quickly and accuratelyidentifies the location of a fault.

SUMMARY

The following discussion describes a method for identifying a locationof a fault in an electrical power distribution network, where thenetwork includes a power source, at least one electrical line, a numberof spaced apart utility poles supporting the electrical line, and atleast one switching device in the electrical line that is operable toprevent a power signal from flowing through the switching device inresponse to detecting the fault. The method includes identifying animpedance of the electrical line between each pair of adjacent utilitypoles downstream of the switching device, measuring a voltage and acurrent of the power signal at the switching device during the fault,but before the switching device prevents the power signal from flowingtherethrough, and estimating a voltage at each of the utility polesdownstream of the switching device using the impedance of the electricalline between the utility poles and the measured voltage and currentduring the fault. The method calculates a reactive power value at eachof the utility poles using the estimated voltages, where calculating areactive power value includes compensating for distributed loads alongthe electrical line that consume reactive power during the fault, anddetermines the location of the fault based on where the reactive powergoes to zero along the electrical line.

Additional features of the disclosure will become apparent from thefollowing description and appended claims, taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified schematic illustration of an electrical powerdistribution network;

FIG. 2 is an illustration of an electrical power distribution networkincluding one recloser on an electrical line with a fault and anotherrecloser on an electrical line connected to the line with the fault;

FIG. 3 is an illustration of an electrical power distribution networkincluding a first recloser on an electrical line with a fault, a secondrecloser on an electrical line connected to the line with the fault, anda third recloser on another electrical line connected to the line withthe fault;

FIG. 4 is an illustration of an electrical power distribution networkincluding two reclosers and a transformer on an electrical line with afault; and

FIG. 5 is an illustration of an electrical power distribution networkincluding two reclosers on an electrical line without a fault and anelectrical line with a fault connected to the line without the fault.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The following discussion of the embodiments of the disclosure directedto a method for identifying a fault location in an electrical powerdistribution network is merely exemplary in nature, and is in no wayintended to limit the invention or its applications or uses.

FIG. 1 is a schematic type diagram of an electrical power distributionnetwork 10 including an electrical substation 12 that steps down highvoltage power from a high voltage power line (not shown) to mediumvoltage power, a three-phase feeder line 14 that receives a mediumvoltage power signal from the substation 12, and a lateral line 16 thatreceives the medium voltage power signal from the feeder line 14. Themedium voltage power signal is stepped down to a low voltage signal by anumber of distribution transformers 18 strategically positioned alongthe lateral line 16, and the low voltage signal is then provided to anumber of loads 20 represented here as homes. The network 10 alsoincludes loads 20 connected to the feeder line 14 that are serviced by adistribution transformer 18.

The network 10 includes a number of reclosers of the type referred toabove provided at certain intervals along the feeder line 14. In thisexample, the network 10 includes an upstream recloser 24 and adownstream recloser 26, where the upstream recloser 24 receives themedium voltage signal from the substation 12 on the feeder line 14before the downstream recloser 26. Although only shown as a single line,the feeder line 14 would include three lines, one for each phase, wherea separate recloser would be provided in each line. A number of utilitypoles 22 are provided along the feeder line 14 and the lateral line 16,where the reclosers 24 and 26 would be mounted on certain ones of thepoles 22. The recloser 24 includes a relay or interrupter switch 30 foropening and closing the recloser 24 to allow or prevent current flowtherethrough on the feeder line 14. The recloser 24 also includes asensor 32 for measuring the current and voltage of the power signalpropagating on the feeder line 14, a controller 34 for processing themeasurement signals and controlling the position of the switch 30, and atransceiver 36 for transmitting data and messages to a control facility(not shown) and/or to other reclosers and components in the system 10.The recloser 26 would include the same or similar components as therecloser 24. The configuration and operation of reclosers of this typeare well understood by those skilled in the art.

The lateral line 16 includes a fuse 38 positioned between the feederline 14 and the first load 20 on the lateral line 16 proximate to a taplocation where the lateral line 16 is connected to the feeder line 14.The fuse 38 is an independent electrical device that is not incommunication with other components or devices in the network 10, wherethe fuse 38 creates an open circuit if an element within the fuse 38heats up above a predetermined temperature as a result of high faultcurrent so as to prevent short-circuit faults on the lateral line 16from affecting other parts of the network 10. In order for voltagestability purposes, the voltage on the feeder line 14 and the lateralline 16 needs to be accurately controlled. For those locations in thenetwork 10 where voltage corrections are necessary to boost the voltageto maintain voltage stability, a voltage regulator 42 is provided in thefeeder line 14, which basically measures the voltage on the line 14 andemploys a transformer 44 to boost the voltage if it drops below apredetermined value. Alternately, the voltage regulator 42 can convertmedium voltage to low voltage, or instead of stepping down the voltageto the desired voltage level, it may step the voltage down to a valuejust above the desired voltage value. In addition to the voltageregulator 42, the power distribution network 10 also employs a capacitor46 positioned on the feeder line 14 to help regulate the voltagethereon, where the capacitor 46 is a load that generates or suppliesreactive power. Without the capacitor 46, all of the reactive power onthe line 14 would be provided by the substation 12, where significantlosses of the reactive power would occur the farther the load 20 is fromthe substation 12.

A fault location 28 is shown on the feeder line 14 between the reclosers24 and 26, which creates a short-circuit or near short-circuit and thusa high fault current. The electrical path of a fault current includesall of the electrical wires and conductors between the substation 12 andthe fault location 28. Along this fault path during the high faultcurrent, the voltage of the power signal on the line 14 drops graduallyfrom the substation 12 to the fault location 28, where the rate ofvoltage drop depends on the magnitude of the fault current and theimpedance Z of the lines 14 and 16, and where the voltage on the line 14at the fault location 28 meets certain conditions, for example, theline-to-ground voltage is zero for line-to-ground faults and theline-to-line voltage is zero for line-to-line faults.

From this understanding, fault location schemes have been devised in theart for calculating the possible locations of a fault on an electricalline by using the known impedance Z of the line and the voltage andcurrent measurements provided by the reclosers along the fault path.Generally in these types of fault location schemes, the measured currentbefore the fault occurs is used to determine the amount of loaddownstream of the recloser, and voltage measurements and estimations areused during the fault as discussed herein, which provides a generallocation of the fault within 50-100 milliseconds of the fault occurring.It is noted that the impedance Z of the line 14 or 16 may be differentbetween the poles 22 depending on a number of factors, such as wirematerial, wire diameter, span length, height of the utility poles, etc.,or the impedance Z could be the same or nearly the same for all of thespans between the poles 22. The reclosers 24 and 26 are able tocommunicate with each other so that the first recloser upstream of thefault location 28 is known to be the last recloser where the faultcurrent and voltage can be measured, where that recloser can be openedso that power is still able to be provided upstream of it.

For the example shown in FIG. 1, the recloser 24 is the first upstreamrecloser from the fault location 28. Since the impedance Z of the feederline 14 and the lateral line 16 are usually known for each span of thelines 14 and 16 between the utility poles 22 downstream of the recloser24, the voltage and current can be estimated at each of the utilitypoles 22 using the measured voltage and current at the recloser 24during the fault, where the voltage will continue to decrease to thefault location 28, where it will be at or near zero. Specifically, sincethe voltage V₀ and the current I₀ are measured at the recloser 24 duringthe fault, but before the switch 30 has opened, and the impedance Z ofthe feeder line 14 and the lateral line 16 is known in each span betweenthe utility poles 22, the voltage at each utility pole 22 can beestimated as V₁=V₀−Z₁I₀, V₂=V₁−Z₂I₀, V₃=V₂−Z₃I₀, etc., where V₁ is theestimated voltage at the first utility pole 22 downstream from therecloser 24, V₂ is the estimated voltage at the second utility pole 22downstream of the recloser 24, V₃ is the estimated voltage at the thirdutility pole downstream of the recloser 24, Z₁ is the impedance of thefeeder line 14 between the recloser 24 and the first utility pole 22, Z₂is the impedance of the feeder line 14 between the first and secondutility poles, and Z₃ is the impedance of the feeder line 14 between thesecond and third utility poles. Thus, the voltage is estimated at eachof the poles 22 in this manner until the estimated voltage begins toincrease. Since the recloser 24 knows the locations of the utility poles22 and their distances from the recloser 24, the general fault location22 can be determined. It is noted that the impedance Z used in thesecalculations need not be overly precise because there is a comparisonbetween two values that are computed based on the same impedance Z.

The above described method for determining the fault location 28 assumesthat the fault is a direct short-circuit and has no impedance Z.However, a typical fault will not cause a direct short-circuit, and thusthere will be some impedance Z at the fault location 28 that is allresistive, which acts to generate heat and create a voltage drop.Reactive power Q can be calculated at the recloser 24 using the equationQ₀=imag(I₀*V₀), where I₀ and V₀ are complex numbers, * is a conjugateoperator, and imag is the imaginary part of a complex number. Thereactive power Q can be estimated at each of the utility poles 22 basedon the estimated voltage determined above, specifically Q₁=imag(I₀*V₁),Q₂=imag(I₀*V₂), Q₃=imag(I₀*V₃), etc. Since I₀ is the fault current, thereactive power calculations are valid as long as the pole 22 for whichthe reactive power Q is calculated is upstream of the fault location 28.At the fault location 28, the reactive power Q is calculated as zerosince the fault only draws real power, and downstream of the faultlocation, the reactive power Q becomes negative. Since the fault may notbe directly at a pole location, the estimated location will be in thespan between the last pole 22 where the reactive power Q is positive andthe first pole where the reactive power Q is negative.

Once the span between two of the utility poles 22 is identified as thelocation where the reactive power goes to zero and thus where the faulthas occurred, then the following equation can be used to identify wherein that span the fault actually is, where Q is the estimated reactivepower at the last utility pole 22 before the fault location 28, I is thefault current, X is the inductive component of the line impedance Z, andl is the distance from the recloser 24 to the fault location 28.

Q=lX _(line/mile) I ²  (1)

The voltage measured at the recloser 26 during the fault is basicallythe same as the voltage at the fault location 28, which is at or nearzero. Because of the high sample rate, the downstream recloser 26 willsee the voltage drop at the time that the fault occurs. As the faultcurrent travels to the fault location 28 from the substation 12 thevoltage drop at each of the utility poles 22 will be significant, butonce the utility poles 22 are off of the fault path, then the voltagedrop at each of the utility poles 22 will be minimal because the faultcurrent is no longer present. Therefore, the downstream recloser 26 canprovide a proximate voltage measurement at the fault location 28 if itis on the feeder line 14 or a proximate voltage measurement where thelateral line 16 connects to the feeder line 14 if the fault is on thelateral line 16.

For simplicity, the above discussion assumes that only one phase of thethree-phase lines is faulted. The fault location method, however, isapplicable for faults involving two or three phases. For example, withthe voltage based approach, a phase-to-phase fault would be identifiedat the point where the phase-to-phase voltage is at or near zero. Withthe reactive power based approach, a phase-to-phase fault would beidentified at the point where the sum of reactive power across allfaulted phases is zero or negative.

Synchronized measurements from the downstream recloser 26 so that aphasor comparison can be made will lead to better performance. However,the fault location detection methods described herein do not assumesynchronized measurements. In the absence of synchronized measurements,only the voltage magnitude can be compared. Alternatively, the angledifference can be estimated by comparing all three-phase voltages.

The fault location detection process based on impedance Z as discussedabove has a number of disadvantages that may not allow the technique toaccurately determine the fault location 28. For example, the process issusceptible to inaccuracies as a result of line impedance errors, loadson the network, taps from voltage regulators, sensor errors, harmonics,etc. Various solutions to some of these issues are discussed below.

The discussion above assumes that the fault location 28 acts as aresistive element to ground where there is only a small amount of realpower and no reactive power, as discussed. However, in reality there aretypically loads, represented by load 40, downstream of the faultlocation 28 that consume both real and reactive power so that they aredrawing some reactive power at the fault location 28 during the fault.In addition, when power goes through an inductor there is loss ofreactive power, and those loads 20 that are upstream of the faultlocation 28 also are consuming reactive power when the fault occurs.Hence, in order to provide a more accurate determination of the faultlocation 28 based on the location where the reactive power goes to zeroin the line 14, a load compensation factor needs to be employed tocompensate for the upstream loads 20 and the downstream loads 40 thatconsume reactive power during the fault. However, the power draw of theloads 20 and 40 is not an available value that could be used to provideload compensation to more accurately identify the fault location 28.Therefore, the load compensation factor would need to be determinedbased on how much power goes through the recloser 24 before the faultand during the fault, where the measurement of the power before thefault is used to estimate how much power the loads 20 and 40 areconsuming downstream of the recloser 24 during the fault.

The present disclosure describes a technique for calculating the loadcompensation factor by measuring the power flow through the upstreamrecloser 24 before the fault occurs and during the fault. Before thefault occurs, all of the power from the recloser 24 is used to power theloads 20 and 40 downstream of the recloser 24. When the fault occurs,and the voltage drops along the feeder line 14, the loads 20 and 40 willbehave differently as a result of that voltage drop. In order toestimate the reactive power draw of the loads 20 and 40 during the faultso that that it can be removed from the calculation of the reactivepower to identify the fault location 28, it is necessary to determinewhether the measured voltage at the recloser 24 during the fault is usedor the voltage at the fault location 28 is used to determine how muchload is connected to the line 14 during the fault. In other words, it isnecessary to determine how much of the fault current is being used topower the loads 20 during the fault, where that amount of current canthen be removed from the estimation of the voltage at the poles 22 thatis used to identify where the reactive power goes to zero to determinethe location 28 of the fault.

According to one embodiment, the load compensation technique determineshow much load is connected to each of the utility poles 22 that includesa transformer 18, which is provided by the utility, but is not availableat every point in time. However, the utility does provide the size ofeach transformer 18 in the network 10, where it is assumed that the sizeor rating of the transformer 18 is based on the amount of load it needsto support. More particularly, the size of the distribution transformers18 would depend on the size and number of the loads 20 it serves, wherethe larger the load 20, the higher the rating of the transformer 18.When a fault occurs, a graph search of all of the transformers 18downstream of the recloser 24 is performed and the size of thosetransformers 18 is added up to obtain a cumulative transformer size,which provides an estimate of the amount of power flowing through therecloser 24 before the fault. Once the cumulative transformer size isobtained, then a utilization ratio is determined that is a prefaultpower P_(prefault) divided by the cumulative transformer size, whichdetermines an average of how much power each of the transformers 18 isdrawing before the fault, where the prefault power P_(prefault) is thepower calculated by the recloser 24 based on the current and voltagemeasurements before the fault.

For each pole 22 that includes a distribution transformer 18, a nominalload power is then determined as the utilization ratio times the size ofthe transformer 18 on that pole 22. Next, the voltage is estimated atevery pole 22 during the fault using the measured current and impedanceZ in the manner discussed above. Then, equation (2) below is used todetermine a fault load power P_(fault) during the fault at each pole 22that includes a transformer 18.

$\begin{matrix}{{P_{fault} = {\left( \frac{v_{fault}}{v_{{nom}\; {inal}}} \right)^{n}P_{prefault}}},} & (2)\end{matrix}$

where v_(fault) is the estimated voltage at the fault location 28 duringthe fault, v_(nominal) is the voltage at the recloser 24 before thefault, and n is an exponential that is determined by experimentation,where n=2 for a constant impedance, n=1 for a constant current and n=0for constant power.

The load power P_(fault) during the fault is divided by the voltagecalculated at that pole 22 to obtain the current going to the loads 20serviced by that pole 22. Therefore, for each estimation of the voltageat each of the poles 22, instead of using the current I₀ for calculatingthat estimation as discussed above, the amount of current drawn by theloads 20 upstream of the pole 22 is subtracted from the current I₀ in acumulative manner as the estimation of the voltage at each polecontinues downstream of the recloser 24 to more accurately identify thelocation 28 of the fault. More particularly, the reactive power Q iscalculated at each of the poles 22 in the manner discussed above asQ=imag((I₀*−I_(c)*)V), where I_(c) is the cumulative current servicingthe loads 20 at that pole 22 and the loads 20 upstream of that pole 22during the fault. This process is also performed for the loads 40downstream of the fault location 28.

As mentioned the capacitor 46 provides a large contribution of reactivepower at a particular location in the network 10, which also needs to becompensated for when determining the fault location 28. Thiscompensation can also be provided by the fault power P_(fault) inequation (2) as the capacitor 46 is well characterized, where the valuen can be determined, and thus the voltage dependency of the capacitor 46can be readily calculated. The capacitor 46 will also be positioned onone the utility poles 22, and therefore the power draw by the capacitor46 can be removed from the measured current I₀ as part of cumulativeremoval of the current in addition to the transformers 18 in the mannerdiscussed above.

Sometimes the capacitor 46 may be switched off because lower loaddemands do not require as much power, where the reactive power Qgenerated by the capacitor 46 is returned to the substation 12. Forexample, during the daytime and evening hours when the power demand isusually high, the utility may turn on the capacitor 46 to deliver thedesired reactive power to the loads 20, and then may turn off thecapacitor 46 at night time when the demand is low to save cost andprovide efficiency. However, the state of the capacitor 46 is not knownto the recloser 24 because there is no communication therebetween.

The fault location detection scheme discussed above may identifymultiple possible fault locations on the various lines depending on howthey are configured. More particularly, the number of the utility poles22 and the spans therebetween will be different depending on whether thefault is on a certain one of the lines, where multiple general faultlocations may be identified. However, a proximate distance from therecloser 24 to the fault location can be provided regardless of whatline the fault is on. Further, the voltage measured by the downstreamrecloser 26 will be approximately the same as the voltage at thelocation where the fault is occurring if it is on the feeder line 14 orthe voltage at the location that the fault current last occurred on thefeeder line 14 if the fault is on the lateral line 16. As will bediscussed in detail below, the present disclosure proposes employingmultiple reclosers that measure voltage and current to eliminatepossible fault locations that are not the actual fault location.

FIG. 2 is a simple illustration of an electrical power distributionnetwork 70 illustrating this embodiment of the disclosure. The network70 includes a main electrical line 72, a secondary line 74 tapped off ofthe main line 72 at tap location 76 and a secondary line 78 tapped offof the main line 72 at tap location 80. The main line 72 includes arecloser 82 and a number of utility poles 84, the secondary line 74includes a recloser 86 and a number of utility poles 88, and thesecondary line 78 includes a recloser 90 and a number of utility poles92.

By using the voltage estimation process at each of the poles discussedabove to determine the location of a fault by employing the impedance ofthe lines 72, 74 and 78, the process could identify locations 96, 98 and100 as possible fault locations, where in this example, the faultlocation 98 is the actual location of the fault. For this specificexample, the recloser 82 measures the fault current when the faultoccurs, but the reclosers 86 and 90 would not measure the fault currentbecause they are not on the fault path, namely, the line 72. When thefault occurs, the recloser 86 on the line 74 is upstream of the possiblefault location 96, but does not measure a fault current because it isnot on the fault path, and thus, it is known that the location 96 is notthe actual fault location. However, because the recloser 90 isdownstream of the possible fault location 100, that location cannot beimmediately eliminated as the actual fault location even though it willnot measure the fault current because it is not on the fault path.

The voltage at the tap location 80 can be estimated based on themeasurement of the current and voltage at the recloser 82 during thefault and the line impedance Z between the poles 84 in the mannerdiscussed above. If the fault is at the fault location 98, then thecurrent measured by the recloser 90 will be much less than the faultcurrent, and if the fault is at the location 100, then the currentmeasured by the recloser 90 during the fault will be near zero, butstill measurable. These different current measurements depending onwhether the fault is at location 98 or 100 can be used to estimate thevoltages at the poles 84 and 92 using the known impedance values by therecloser 90 in the manner discussed above to help identify the locationof the fault. The voltage at the tap location 80, the last pole 84before the fault location 98 and the poles 92 on both sides of the faultlocation 100 can be estimated by both of the reclosers 82 and 90 andthose various voltages can be compared to each other. If the voltagesestimated by the reclosers 82 and 90 is the same at the tap location 80,then it is known that the fault location 98 is the actual faultlocation. However, if the voltage calculated by the reclosers 82 and 90is the same at the location 100, then that is the actual fault location.

Often times the impedance Z of the line provided by the utility is notaccurate and thus will not give accurate voltage estimations at thepoles for determining fault locations as discussed above. According toone embodiment of the disclosure, the current and voltage measured bythe reclosers 24 and 26 during the fault can be used to provide a moreaccurate estimate of the impedance Z of the feeder line 14 therebetween,and that estimation of the impedance Z can be compared to the impedanceZ of the line 14 provided by the utility company to determine itsaccuracy. An error between the calculated impedance Z and the givenimpedance Z can be used to more accurately determine the location 28 ofthe fault by correcting the given impedance Z of the line 14 downstreamof the recloser 24 where the voltages are estimated. For example, if thecalculation of the line impedance Z between the reclosers 24 and 26determines that the calculated impedance Z and the given impedance Z hasan error of 10%, that 10% correction can then be used in thecalculations discussed above when estimating the voltage at the poles22, which gives a more accurate location of the fault based on when thevoltage goes to zero or near zero, where the impedance Z is giventypically in ohms per mile.

FIG. 3 is a simple illustration of an electrical power distributionnetwork 50 that illustrated the impedance Z correction embodiment forproviding a more accurate determination of a fault location. The network50 includes a first electrical line 52 and a second electrical line 54connected to the first line 52 at a tap location 56, where a fault hasoccurred at location 58 in the line 52, and where the lines 52 and 54can be feeder lines or lateral lines. A recloser 60 is provided in thefirst line 52 upstream from the fault location 58 and a recloser 62 isprovided in the second line 54, and is not on the fault path. A numberof utility poles 64 are provided in the line 52 and a number of utilitypoles 66 are provided in the line 54.

Because the fault is not located in the lines 52 and 54 between thereclosers 60 and 62, the impedance Z of the lines in that section of thenetwork 50 can be accurately determined because the measured voltage andcurrent are provided at the reclosers 60 and 62. The voltage on the line52 will significantly decrease from the recloser 60 to the tap location56 during the fault and the recloser 62 will measure that voltage duringthe fault. The voltage is estimated by the recloser 60 at the taplocation 56 in the manner discussed above using the given impedance Z,and that voltage is compared to the voltage measured by the recloser 62during the fault, where the difference in the estimated voltage and themeasured voltage is a result of an error of the impedance Z in the line52 used to estimate the voltage at each pole 64. In other words, becausethe impedance between adjacent poles 64 and adjacent poles 66 isprovided, and the voltage is measured at the recloser 60 and therecloser 62, the estimation of the voltage at the tap location 56 can beused to provide the error that identifies a correction for theimpedance. The voltage measured by the recloser 62 minus the estimatedvoltage at the last pole 64 before the fault location 58 is equal to thecurrent measured by the recloser 62 times the impedance Z in the line 54between the recloser 62 and the tap location 56. Therefore, theimpedance Z of the line 52 can be corrected in the line 52 after the taplocation 56 based on the actual impedance calculation and thatcorrection can be applied to the section of the line 52 between the taplocation 56 and the fault location 58.

If a voltage regulator 68 is provided in the line 52 downstream of therecloser 60, but upstream of the fault location 58, the estimates of thevoltage downstream of the voltage regulator 68 may no longer beaccurate, and corrections need to be made in order to more accuratelydetermine the location 58 of the fault. By comparing the voltage at thetap location 56 to the measured voltage at the recloser 62 will allowthe recloser 60 to know how much the voltage regulator 68 has stepped upthe voltage, which can be employed in the voltage estimationcalculations downstream of the tap location 56. Further, it is possibleto use the comparison of those two voltages to identify whether thedifference in the voltages is a result of the error in the impedance Zor caused by the increase in voltage provided by the voltage regulator68.

The present disclosure also describes a technique for identifying thelocation of a fault if the impedance Z of the feeder line 14 between thepoles 22 is not known. FIG. 4 is a simple illustration of a distributionnetwork 110 illustrating this embodiment. The network 110 includes atransformer 112 that represents the large power transformer in thesubstation 12 that steps down the high voltage on transmission line 114from a power plant 116 on the transmission side of the transformer 112to a medium voltage on line 118 on the distribution side of thetransformer 112, where the voltage on the transmission side does notchange as a result of faults that may occur on the distribution side. Afirst recloser 120 and a second recloser 122 are provided in the line118 and utility poles 124 are provided along the line 118, where a faultlocation 126 is identified downstream of the recloser 122. The voltageand current are measured by the reclosers 120 and 122 and the voltagesare estimated at the downstream poles 124 from the reclosers 120 and 122during the fault in the manner discussed above, where the voltagemeasured by the reclosers 120 and 122 before the fault is the same oralmost the same as the voltage on the transmission line 114. From thesemeasurements, the impedance Z₁ of the line 118 between the substation112 and the first recloser 120 and the impedance Z₂ of the line 118between the substation 112 and the second recloser 122 can be determinedas:

$\begin{matrix}{{Z_{1} = \frac{V_{ld} - V_{ft1}}{I_{ft}}},} & (3) \\{{Z_{2} = \frac{V_{ld} - V_{ft2}}{I_{ft}}},} & (4)\end{matrix}$

where V_(id) is the voltage on the transmission line 114, V_(ft1) is thevoltage measured by the recloser 120 during the fault, V_(ft2) is thevoltage measured by the recloser 122 during the fault, and I_(ft) is thefault current measured by the reclosers 120 and 122.

The impedances Z₁-Z₂ are subtracted to get the impedance of the line 118between the reclosers 118 and 120, and that value is divided by thedistance between the reclosers 118 and 120 to give an impedance Z perdistance, such as per mile or per kilometer. Therefore, that impedance Zper distance can be assumed to be the same for the line 116 downstreamof the recloser 122, and the location of the fault 124 can be determinedby estimating the voltage at each pole 124 downstream of the recloser122 until the reactive power goes to zero in the manner discussed above.If the impedance of the transformer 112 is known, then only a single oneof the reclosers 120 or 122 is needed in the line 116 to estimate theimpedance Z per distance, where the impedance Z calculated by equation(3) is subtracted from the transformer impedance to obtain that value.

FIG. 5 is a simple illustration of a distribution network 130illustrating the case where the location of a fault can be identifiedwithout knowing the line impedance, where the fault is on a line thatdoes not include a recloser. The network 130 includes a feeder line 132having a first recloser 134 and a second recloser 136 and including anumber of utility poles 138. A secondary or lateral line 140 is tappedfrom the line 132 at tap location 142, and includes utility poles 144,where the fault is at location 146 on the line 140. In this example, thevoltage at the tap location 142 during the fault is the same or nearlythe same as the voltage measured by the second recloser 136 during thefault. The impedance Z of the section of the line 132 between the firstrecloser 134 and the tap location 142 can then be determined as voltageV₁ measured by the recloser 134 during the fault minus voltage V₂measured by the recloser 136 during the fault divided by the faultcurrent I as (Z=(V₁-V₂)/I). Since the distance from the recloser 134 tothe tap location 142 is known, the impedance Z per distance can beobtained, and that value can be used to obtain the location 146 of thefault by estimating the voltage at each pole 124 downstream of therecloser 134 until the reactive power goes to zero in the mannerdiscussed above.

The foregoing discussion discloses and describes merely exemplaryembodiments of the present disclosure. One skilled in the art willreadily recognize from such discussion and from the accompanyingdrawings and claims that various changes, modifications and variationscan be made therein without departing from the spirit and scope of thedisclosure as defined in the following claims.

What is claimed is:
 1. A method for identifying a location of a fault inan electrical power distribution network, said network including a powersource, at least one electrical line, a number of spaced apart utilitypoles supporting the at least one electrical line, and at least oneswitching device in the electrical line, said at least one switchingdevice being operable to prevent a power signal from flowing through theswitching device in response to detecting the fault, said methodcomprising: identifying an impedance of the at least one electrical linebetween each pair of adjacent utility poles downstream of the at leastone switching device; measuring a voltage and a current of the powersignal in the at least one switching device during the fault, but beforethe switching device prevents the power signal from flowingtherethrough; estimating a voltage at each of the utility polesdownstream of the at least one switching device using the impedance ofthe electrical line between the utility poles and the measured voltageand current during the fault; calculating a reactive power value at eachof the utility poles using the estimated voltages, wherein calculating areactive power value includes compensating for distributed loads alongthe electrical line that consume reactive power during the fault; anddetermining the location of the fault based on where the reactive powervalue goes to zero along the at least one electrical line.
 2. The methodaccording to claim 1 wherein compensating for the distributed loadsincludes estimating the reactive power that the distributed loadsconsume based on a cumulative power rating size of a plurality ofdistribution transformers that provide power to the distributed loadsdownstream of the at least one switching device.
 3. The method accordingto claim 2 wherein determining the cumulative power rating size of thetransformers includes doing a graph search of all of the transformersdownstream of the at least one switching device, and adding the sizestogether.
 4. The method according to claim 2 wherein compensating forthe distributed loads includes determining a prefault power value from ameasured current and voltage by the at least one switching device beforethe fault, determining a utilization ratio that is the prefault powervalue divided by the cumulative transformer size, calculating a nominalload power value at each of the utility poles that includes atransformer as the utilization ratio multiplied by the size of thetransformer on that pole, using the estimated voltage and the nominalload power value at the pole to determine a fault load power valueduring the fault, dividing the fault load power value by the estimatedvoltage to obtain a current draw value at the pole, and cumulativelyreducing the current that is used to estimate the voltage at each polebased on the current draw value used to supply the loads.
 5. The methodaccording to claim 4 wherein determining the fault load power valueduring the fault includes using the equation:$P_{fault} = {\left( \frac{v_{fault}}{v_{{nom}\; {inal}}} \right)^{n}P_{prefault}}$where P_(fault) is the fault load power value, P_(prefault) is theprefault power value, v_(fault) is the measured voltage at the faultlocation during the fault, v_(nominal) is the voltage before the fault,and n is an exponential that is determined by experimentation, where n=2for constant impedance, n=1 for constant current and n=0 for constantpower.
 6. The method according to claim 1 wherein calculating a reactivepower value includes compensating for a capacitor provided in theelectrical line downstream of the at least one switching device thatprovides reactive power on the electrical line.
 7. The method accordingto claim 6 wherein compensating for the capacitor includes calculating afault power at the capacitor.
 8. The method according to claim 1 whereinestimating the voltage at each pole includes using the equation:Q=imag(I*V) where Q is reactive power, I is the measured fault currentand V is the estimated voltage.
 9. The method according to claim 1wherein identifying the fault location includes identifying the locationof the fault in a span between utility poles using the equation:Q=lX _(line/mile) I ² where Q is the estimated reactive power at thelast utility pole before the fault location, I is the fault current, Xis the inductive component of the line impedance Z, and l is thedistance from the at least one switching device to the fault location.10. The method according to claim 1 wherein the power source is anelectrical substation and the electrical power distribution network is amedium voltage power distribution network.
 11. The method according toclaim 1 wherein the at least one switching device is a recloser.
 12. Themethod according to claim 1 wherein the at least one electrical line isone phase of three-phase lines in a feeder line.
 13. A method foridentifying a location of a fault in an electrical power distributionnetwork, said network including a substation, a feeder line, a number ofspaced apart utility poles supporting the feeder line, and a recloser inthe feeder line on one of the poles, said recloser being operable toprevent a power signal from flowing through the recloser in response todetecting the fault, said method comprising: identifying an impedancevalue of the feeder line between each pair of adjacent utility polesdownstream of the recloser; measuring a voltage and a current of thepower signal in the recloser during the fault, but before the recloserprevents the power signal from flowing therethrough; estimating avoltage at each of the utility poles downstream of the recloser usingthe impedance of the feeder line between the utility poles and themeasured voltage and current during the fault; calculating a reactivepower value at each of the utility poles using the estimated voltages,wherein calculating the reactive power value includes compensating fordistributed loads along the feeder line downstream of the recloser thatconsume reactive power during the fault based on a cumulative powerrating size of a plurality of distribution transformers that providepower to the distributed loads; and determining the location of thefault based on where the reactive power value goes to zero along thefeeder line.
 14. The method according to claim 13 wherein compensatingfor the distributed loads includes determining a prefault power valuefrom a measured current and voltage by the at least one switching devicebefore the fault, determining a utilization ratio that is the prefaultpower value divided by the cumulative transformer size, calculating anominal load power value at each of the utility poles that includes atransformer as the utilization ratio multiplied by the size of thetransformer on that pole, using the estimated voltage and the nominalload power value at the pole to determine a fault load power valueduring the fault, dividing the fault load power value by the estimatedvoltage to obtain a current draw value at the pole, and cumulativelyreducing the current that is used to estimate the voltage at each polebased on the current draw value used to supply the loads.
 15. The methodaccording to claim 14 wherein determining the fault load power valueduring the fault includes using the equation:$P_{fault} = {\left( \frac{v_{fault}}{v_{{nom}\; {inal}}} \right)^{n}P_{prefault}}$where P_(fault) is the fault load power value, P_(prefault) is theprefault power value, v_(fault) is the measured voltage at the faultlocation during the fault, v_(nominal) is the voltage before the fault,and n is an exponential that is determined by experimentation, where n=2for constant impedance, n=1 for constant current and n=0 for constantpower.
 16. The method according to claim 13 wherein calculating areactive power value includes compensating for a capacitor provided inthe electrical line downstream of the at least one switching device thatprovides reactive power on the electrical line.
 17. The method accordingto claim 16 wherein compensating for the capacitor includes calculatinga fault power at the capacitor.
 18. The method according to claim 13wherein estimating the voltage at each pole includes using the equation:Q=imag(I*V) where Q is reactive power, I is the measured fault currentand V is the estimated voltage.
 19. The method according to claim 13wherein identifying the fault location includes identifying the locationof the fault in a span between utility poles using the equation:Q=lX _(line/mile) I ² where Q is the estimated reactive power at thelast utility pole before the fault location, I is the fault current, Xis the inductive component of the line impedance Z, and l is thedistance from the at least one switching device to the fault location.20. A system for identifying a location of a fault in an electricalpower distribution network, said network including a power source, atleast one electrical line, a number of spaced apart utility polessupporting the at least one electrical line, and at least one switchingdevice in the electrical line, said at least one switching device beingoperable to prevent a power signal from flowing through the switchingdevice in response to detecting the fault, said method comprising: meansfor identifying an impedance of the at least one electrical line betweeneach set of adjacent utility poles downstream of the at least oneswitching device; means for measuring a voltage and a current of thepower signal in the at least one switching device during the fault, butbefore the switching device prevents the power signal from flowingtherethrough; means for estimating a voltage at each of the utilitypoles downstream of the at least one switching device using theimpedance of the electrical line between the utility poles and themeasured voltage and current during the fault; means for calculating areactive power value at each of the utility poles using the estimatedvoltage that includes compensating for distributed loads along theelectrical line that consume reactive power during the fault; and meansfor determining the location of the fault based on where the reactivepower value goes to zero along the at least one electrical line.